1. Field of the Invention
This invention relates to production of geothermal brines and, more specifically, to utilization of gases dissolved in and associated with such brines, to effect such production. The invention also relates to the recovery of heat energy, water and chemicals from geothermal aquifers.
2. Description of the Prior Art
The prior art pertinent to the present invention is believed to be limited to two categories: (1) production of geothermal brines (by means other than gas-lifting) and (2) gas-lifting of water and/or petroleum from wells at ordinary subterranean temperatures.
The known art(s) involved in the utilization of geothermal brines is summarized in number 12 of a series of publications by the Unesco Press on earth sciences; Geothermal Energy, Review of Research and Development (The Unesco Press, 7 Place de Fontenoy, 75700 Paris, France; (1973)).
Brines obtained from naturally heated aquifers have been utilized for various purposes since at least as early as ancient Rome. In recent times, geothermal brines having temperatures up to about 120.degree. C. have been used, or proposed to be used, for such varied purposes as the following (listed in order of increasing temperature requirements): fish hatching or farming, de-icing, operation of mines and mills in cold climates, swimming pools, biodegradation processes, fermentation, soil warming, therapeutic baths, mushroom growing, greenhouse operations, animal husbandry, energization of refrigeration equipment, space heating, drying of fish, seaweeds, grasses, vegetables, etc., wood processing, drying and curing of concretes and evaporation or distillation of water from brackish or saline water supplies.
The most dramatic and best known use for geothermal energy is electric power generation, as practiced in Italy, Japan, Iceland, New Zealand, Mexico and the United States (California). In some locations, "dry" steam, produced as such from geothermal wells, is employed for this purpose. In other locations, wet steam, present as such in a geothermal formation or formed by flashing of hot brines, is used. In the latter instance, flashing may occur in the formation, in the well or after egress from the well head, depending on formation conditions and the mode of operation. Flashing necessarily entails a temperature drop and an increase in solute concentration in the liquid phase. Thus, precipitation of dissolved minerals often is consequent upon flashing. The resulting deposits constitute an expensive nuisance in surface installations but are a much more serious problem when formed within the formation and/or the well(s). Consequently, it will frequently be desirable to produce a geothermal brine under sufficient pressure that flashing prior to egress is largely avoided. However, geothermal formation pressures usually are not high enough to permit "self production" of brines without at least partial flashing and some "external" lifting agent will ordinarily be required.
Downhole pumps have been used for lifting geothermal brines but considerable difficulties in maintaining bearing lubrication and avoiding electrical problems have been experienced.
It is thus apparent that a better method for lifting geothermal brines which are not under sufficient autogenous pressure to be self-lifting without flashing is needed. To be practical and economic, such a method must not require the use of oxygen-containing gases or gases which are both soluble and expensive.
A complicating factor in any consideration of gas-lifting geothermal brines is the fact that such brines generally are saturated (and associated) with gases, such as carbon dioxide and hydrogen sulfide, which affect the chemical nature and solubilities of certain mineral components of the brines. Precipitation of such components may result if the composition or the pressure on the gas phase of the total geothermal fluid is altered. An additional problem is that severe corrosion problems can be expected to result if an oxygen-containing gas, such as air, is employed for lifting. A further problem is that solubility losses of any inert gases which might be employed for lifting could be prohibitively expensive.
The practice of gas-lifting has heretofore been largely restricted to the use of air, i.e., to "air lift pumping", for obvious reasons of availability and cost. The state of this art has changed little in recent years and is as described by K. E. Brown; "Gas Lift Theory and Practice", Petroleum Publishing Co., (1967).
Air lifting used to be a popular method of pumping liquids but has largely been displaced in many previously favored applications by deep-well (down-hole) centrifugal pumps. The latter pumps are more economical and can handle corrosive and erosive liquids when appropriately designed and fabricated of suitable materials. However, simplicity and the absence of moving parts in contact with the liquid to be pumped remain as outstanding advantages of gas-lifting, particularly where economic considerations are not paramount.